Tree fellers for cutting trees, called feller/bunchers if they have accumulating arms, are well known in the logging industry. In a typical arrangement, a disc saw is carried at the front of a boom of a back hoe type vehicle, that may be a tracked or wheeled vehicle, that has a gasoline or diesel engine. The engine typically drives two or more variable displacement hydraulic pumps, at least one of which is for the drive functions of the vehicle and the other of which is for turning the disc saw. In the past, the engine power useable to drive these two pumps has been determined by the characteristics of the pump and by the load to which the pump was subjected. The displacement of both pumps is manually controlled by the operator with suitable controls provided in the cab. Usually, the saw drive pump is operated at full displacement once the saw is brought up to speed, and the main pump displacement is controlled by the operator, depending on how fast the operator wants to operate the machinery or the loading placed on the machine by the various functions of the machine, with limits placed on it by the system so as not to overload the prime mover. However, there are times when it is desirable to limit the amount of engine power available to drive the saw, so as to make more power available for the other machine functions, such as driving the wheels or track in rough terrain, operating the clamp arms of the saw head in windy conditions, or operating the boom with a large load of trees held by the saw head, or while cutting a tree. This invention is directed toward a new way to divide power between the saw and main pumps in a tree felling machine.